Chain guards for electrically operated hoist pulley blocks



D. M. KING Sept. 12, 1961 CHAIN GUARDS FOR ELECTRICALLY OPERATED HOIST PULLEY BLOCKS Filed NOV. 25, 1958 2 Sheets-Sheet 1 D. M. KING Sept. 12, 1961 CHAIN GUARDS FOR ELECTRICALLY OPERATED HOIST PULLEY BLOCKS 2 Sheets-Sheet 2 Filed Nov. 25, 1958 United States Patent 2,999,623 CHAIN GUARDS FOR ELECTRICALLY OPERATED HOIST PULLEY BLOCKS Donald Mayer King, Argyle Works, Stevenage, England Filed Nov. 25, 1958, Ser. No. 776,329 Claims priority, application Great Britain Nov. 26, 1957 Claims. (Cl. 226-43) This invention relates to chain guards for application to electrically operated hoist pulley blocks and more particularly to chain guards of the kind described in my Patent No. 2,529,084 of November 7, 1950.

In said patent there is described a hoist block chain guard which comprises two rockable arms or like elements arranged about a hoist block sprocket in such a manner as to mask those portions of the chain passing around said sprocket, said elements being normally urged into and maintained in their operative or guard position wherein they will allow free passage of the chain by virtue of the action of resilient means. In a hoist incorporating such a chain guard mechanism it is common practice to provide on the hoist chain at selected points so called limit stops or abutments which project from said chain and are adapted as the latter approaches the limit of its travel in either direction to contact one or other of said arm or like elements thereby to cause displacement of the latter against the action of the resilient means, such displacement in turn resulting in the actuation of a switch and automatic cutting ofi of the hoist motor. The arrangement is also such that one or other of said arms or like elements will also be displaced to effect cutting 011 of the hoist motor in the event that any section of the chain approaching the hoist sprocket becomes kinked, twisted or otherwise distorted.

It is the chief object of the invention to provide an improved chain guard mechanism of the kind indicated above and in accordance therewith each arm or like element of such a mechanism is provided with a relatively light subsidiary lever, tongue or the like which while being mounted for pivotal movement relatively thereto is adapted normally to assume an operative position wherein it will be in the path of any limit stop or abutment carried by the hoist load chain, such subsidiary lever tongue or the like carrying a contact member adapted to cooperate with a switch controlling the operation of the hoist motor and the arrangement being such that any limit stop or abutment on the chain will be effective only to displace the subsidiary lever, tongue or the like thereby to effect cutting oil of the hoist motor, the main arm or like element with which said lever, tongue or the like is associated remaining in its operative position in such circumstances and being dispiaceable to effect cutting off of the hoist motor only in the event that a kinked, twisted or otherwise distorted section of the chain approaches the hoist sprocket.

In order that the said invention may be clearly understood and readily carried into efiect the same will be hereinafter more fully described with reference to the accompanying drawings in which:

FIGURE 1 is a side elevational view of 'a chain guard assembly as applied to an electrically operated hoist pulley block,

FIGURE 2 is a side elevational view of one of the guard elements of the assembly shown in FIGURE 1,

FIGURE 3 is a plan view of the guard element shown in FIGURE 2.

Referring now to the drawings, denotes the chain sprocket of an electrically operated hoist pulley block, such sprocket being adapted to be driven on operation of the hoist motor thereby to impart movement to the hoist chain 11 which passes around said sprocket. each side of the sprocket 10 is a chain guard element Disposed at ice designated generally by 12, such elements each being mounted for pivotal movement about a fixed pivot 13. The guard elements '12 which are so formed as to embrace or shroud portions of the chain as it passes around the sprocket 10 are retained in their operative positions as indicated in FIGURE 1 by means of a pair of springs 14 which serve to provide a resilient coupling between the upper ends thereof, the arrangement being such that either guard element is capable of outward displacement from its'operative position about its pivot 13 against the action of the springs 14. As will be seen from the drawings the ends of the springs 14 are conveniently anchored to transverse pieces 15 formed integrally one with each guard element. J

In the embodiment illustrated each guard element incorporates two spaced side or wing portions 16 which define a passage adapted to accommodate and to allow free movement of the chain as it passes around the sprocket wheel. Disposed between the side or wing portions 16 of each guard element is a lever or tongue 17 which is mounted for pivotal movement about the pivot 13 serving to support the associated guard element. The upper ends of the levers or tongues 17 are interconnected by means of a spring =18 which will serve to maintain said levers or tongues in their normal or operative positions wherein the upper ends thereof will abut the respective transverse pieces 15 of the guard elements. As will be seen the face 19 of each lever or tongue 17 is appropriately profiled to conform to the chain as it passes normally around the sprocket. At its lower part each tongue or lever 17 is formed with a tail portion 20 which overlies and is spaced from a corresponding tail portion 21 on the associated guard element 12. The tail portion 20 of each lever or tongue 17 serves to support an adjustable contact member 22 adapted to cooperate with a switch, indicated generally at 23, arranged in the hoist motor circuit.

The arrangement is such that while each lever or tongue 17 is capable of pivotal movement relatively to its associated guard element 12, outward pivotal movement or displacement of the latter from its operative position will result in a corresponding movement or displacement of said lever or tongue due to the fact that the transverse piece 15 is in contact with the upper end of said lever or tongue.

The construction above described is adapted to operate in the following manner:

When the hoist is at rest or opera-ting normally the guard elements 12 and their associated levers or tongues 17 will assume the positions shown in FIGURE 1. In accordance with usual practice each run of the hoist chain will carry at an appropriate point a limit stop or abutment one such device being indicated diagrammatically at 24 in FIGURE 1. When during operation the hoist is approaching the desired limit of its travel in one direction or the other, the appropriate limit stop or abutment will contact and cause displacement of the lever or tongue 17 of the appropriate chain guard thereby to cause opening of the switch 23 and cutting off of the hoist motor. The arrangement is such that the main guard element 12 will not be displaced in such circumstances and will remain in its operative position. However, in the event of a kinked, twisted or otherwise deformed section of the chain approaching the chain sprocket 10 at any time during operation of the hoist the arrangement is such that the appropriate chain guard element 12 will be displaced. As indicated above displacement of either of the guard elements 12 will result in simultaneous displacement of the associated lever or tongue 17 thereby to cause cutting oflf of the motor.

With the construction above described and illustrated the limit stops or abutments will only be required to displace a relatively light member is. the lever or tongue 17 as opposed to the normal chain guard element 12 and hence a more efficient operation will result than in the case where such stop or abutment is required to displace the whole chain guard 'as has been the practice hitherto.

I claim:

1. In operative association with a chain system including a chain, an abutment on the chain and extending outwardly therefrom, a sprocket engaging and moving the chain in a predetermined alignment with respect to said sprocket, and a control operative to control movement of the chain; an apparatus responsive to said abutment for actuating said control and to deformities in said chain for actuating said control, said apparatus comprising, on opposite sides of said sprocket, a first lever adjacent said chain and sprocket and having a surface facing the chain and sprocket and adapted to accommodate the passage of the chain in said predetermined alignment between the sprocket and said lever, a second lever adjacent said chain and sprocket and operatively disposed with respect to said abutment for being engaged by the latter, said first lever having a shape adapted to permit the free passage of said abutment and being displaceable solely by said chain when the latter deviates from said predetermined alignment, resilient means respectively connecting the first levers and the second levers on opposite sides of said sprocket and urging said levers toward said chain, pivot means supporting the levers whereby the first lever on each side of the sprocket is adapted to be pivoted when said chain deviates from said predetermined alignment and whereby "4 the second lever on each side of the sprocket is adapted to be pivoted independently of the associated first lever by engagement with said abutment, and control actuating means operatively disposed with respect to at least one of said levers on each side of the sprocket and responsive to a pivoting of at least one of said levers on each side of the sprocket to actuate said control.

2. Apparatus 'as claimed in claim 1 wherein said pivot means is a fixed pivot common "to the levers on "one "side of the sprocket.

3. Apparatus as claimed in claim 1 wherein said resilient means comprises a spring coupled to the first levers and a separate spring coupled to the second levers.

4. Apparatus as claimed in claim 1 wherein said pivot means is a fixed pivot common to the levers on one side of the sprocket, said first lever on each side of the sprocket comprising a portion adapted to engage and displace the associated second lever, said control actuating means being mounted on said associated second lever.

5. Apparatus as claimed in claim 1 wherein each said first lever is provided with a central opening accommodating the associated second lever.

References Cited in the file of this patent UNITED STATES PATENTS 2,529,084 King Nov. 7, 1950 FOREIGN PATENTS 143,987 Australia Oct. 26, 1951 954,298 France June 6, 1949 

